The modern day demon
by RosieMck
Summary: Abigail Smith is, on the surface, a quiet, rather ordinary girl. Underneath, she's a psychopath. Caught in the act of murder by Mycroft Holmes she has no other option but to take a deal to avoid prison. As a result she ends up working with the worlds only consulting detective. But how will the high-functioning sociopath cope with the one person he can't read? Sherlock/OC
1. Chapter 1

**Authors note: **I'm afraid none of the characters from the show actually appear in this chapter, and Sherlock himself won't show up for a while. Forgive me! It's a slow build up, but it'll be worth it.

Maybe,

I hope it will be anyway.

Enjoy!

**Chapter One – Psychopathy**

**Psychopath. **A psychopath, the modern day demon. Often when we read of serial killers, child molesters, etc. the scum of our society, the sickest of them are psychopaths. The media portrays them as monsters, psychiatrists describe them as such. But you want to know the truth? What a psychopath really is? Well, for once, the media's _right._

No remorse, no empathy, no concept of consequences, impulsive, no control, all traits of a psychopath. And I hear what you're saying, 'I thought they were cold, calculating, and always had control?' Well, some do.

The men.

The_ female_ psychopath, however, is an entirely different creature. While you may describe the male as emotionally cold, the female by contrast is hot. Red hot. Although the two sexes share the fact that they have no empathy or remorse, the female rather than feeling no emotions what so ever, is ruled by them. Love, lust, anger, and hate. She is also impulsive, or at least, seems that way. She can decide in a split second that she's going to kill someone, and in that time frame we'd assume, thinking like a normal person, that she'd not thought it through.

Well, you'd be wrong.

In that second she's thought through every eventuality and possible consequence, and how to get around it.

No remorse, no empathy, and why would she receive justice for her actions? She was right, of course. On the off chance she was caught, why should she receive consequences, when her actions where correct? _'Oh, he had to die. He didn't tie his shoelaces right.' 'She had to die, she was flirting with my boyfriend.' 'He had to die, his crying was interrupting my sleep…'_

**Psychopath. **Not a word you would in the least associate with Abigail Smith. Abigail, or Abbie as her friends (well, people whom she spoke to,) knew her, was a sweet, rather quiet girl who worked in the local police station as a receptionist. Yes, no one would suspect that underneath her perfect smile and cheerful demeanour that Abbie was _boiling_. She watched them, criminals, murders, coming in to the station after their arrests. And they made her angry. Not for the reason that they made the public angry, for their disgusting, despicable disregard for human life. No, they made Abbie angry because they were sloppy. They were stupid, they were idiots. Abbie loved to look through their cases and rewrite in her head how she would have done it. She took a long time, deliberating, planning on who, how and when she would commit her first murder. When talking to her therapist she let on none of this, of course. She had been diagnosed as psychopathic when she was just three, when she had burned down her family home, nearly killing her mother, father and three brothers. When she was questioned on why she did it, she had responded simply with 'because they had to go.' She was taken into care after that, bounced around a few foster homes, always freaking out her new family with how calmly she could talk about trying to kill her parents, and about how she would kill them, given the chance. Eventually Abbie became a ward of the state. Which suited her just fine. They gave her an apartment of her own in Wirral, with regular visits from social workers to make sure she was ok, a word to the neighbours to watch out for her. She was 12 by this point, and needed no supervision. It didn't take much for the neighbours to leave her alone, after the Rutherford's kitten was found in their blender, having been made into a lumpy, boney soup after Mrs Rutherford insistently and relentlessly tried to get Abbie to come over for dinner, play with her children, be a 'normal' little girl, the neighbours got the message.

After the kitten incident however Abbie was required to go weekly to a new therapist, one with 'special training' who could 'deal better with psychopathy.' This therapist was Mr Ballmer, and Abbie thought he was an idiot. He truly believed that he was the only one to which Abbie confided everything, all she had to do was bat her pretty green eyes at him and he'd melt. 'Expert on psychopathy my ass,' Abbie thought, she was 16 when she'd watched him tear up over her heart-wrenching confession that her father had beat her and her brothers, and she never meant to hurt them but she just wanted it to stop. This was all bullshit of course, 'they had to go' because Abbie wanted to be on her own. She didn't like sharing her toys, her space with anyone. She especially didn't like sharing her parent's attention with her brothers, they were worthless, were so stupid and ordinary and plain, why were her parents bothering with them? So, she figured she'd get new ones. A new family. But none of them worked out either, there were always other children in the house, others to steal her spotlight, so she couldn't stay there. At least living as an emancipated minor, she had the attention of the state. And how she'd loved playing that.

She knew that they were watching her, she could tell in a crowd who had been sent to watch her, and could sense when she was being followed. She loved it, to play games with them, to watch them panic when she'd seem to lead a child away from its parents, or when she was a little older seduce a guy at a bar and make to take him home. She'd never actually done anything, she'd always abandon the child just before it was out of its parent's sight, or get the taxi driver to take her potential bed partner/victim home. But watching the agents go into panic mode was fun.

Well, it was enough anyway.

After her 'confession' to her therapist he released a book, 'Breaking Psychopathy, by Charles Ballmer.' About how through 'therapy and meditation' he had cured a psychopath.

Bullshit.

But it was important for him to think that he had.

It was Abbie's 22nd birthday. She didn't usually celebrate birthdays, she didn't see much point. But today was different. She went to the hair dressers and had a wash, cut and blow dry. Nothing drastic, just a little trim to her naturally curly waist-length brown locks. She then went to the chemists and picked up a bottle of Tylenol, for her 'bad headache.' And then off to the off licence, to pick up a nice bottle of wine.

You see, tonight Abbie had a date. A Mr Oliver Carter, who worked the check-out at the local Tesco's, had invited her over for dinner.

So Abbie brought home the wine, uncorked it, and added nitroglycerin. This, when consumed, would give Mr Carter a headache. She then took out the bottle of Tylenol, and with a scalpel cut open all-bar-one of the capsules, and added cyanide to them.

Not a lot of cyanide, certainly not enough to show up on a drugs test, but enough to react with the alcohol and nitroglycerin in Mr Carter's system.

He would die of a heart attack, and Abbie in no way could be indicted for it.

To combat her own headache from drinking the wine she had the one safe Tylenol capsule in her skirt pocket. She would offer a capsule from the bottle to Oliver Carter, and in less than 5 minutes, he would be dead. She would then call an ambulance in hysterics, and they would get there just too late.

And if any of them did suspect foul play, she had many 'friends' down at the police station. 'Abbie? Sweet little Abbie? The receptionist? Oh no, definitely not. No way could she do that!'

With the testimony of the police force and lack of physical evidence, there was no chance of her going away for this.

So, having sealed the Tylenol capsules and re-corked the wine, Abbie got into her little mini cooper and drove to Oliver Carter's house. He greeted her enthusiastically, she returned the nervous grin he gave her, oh lord how stupid people could be, so easily fooled by a smile. The evening went rather pleasantly, the food was good. They drank the wine he provided first, well, he had most of it. Abbie had found this very agreeable, the more intoxicated he was, the less likely he was notice anything out of the ordinary. Like her taking the un-poisoned Tylenol capsule out of her pocket, rather than the bottle.

After dinner he uncorked the spiked wine, show time.

After they'd finished half their glasses the headaches hit, she smiled very sweetly at him, passing him the already open bottle of Tylenol, her own pill already in hand. He thanked her as he took the bottle, and was about to put the capsule in his mouth when –

"I wouldn't take that if I were you."


	2. Chapter 2

**Authors note: **This chapter's a little shorter than the previous one, but at least we've got Mycroft in this one! Next Chapter we'll see Sherlock,

so, hope you enjoy!

**Chapter Two – The Deal**

Abbie's brain shot into over drive, 'who the fuck is this man in the doorway, with his smart suit and umbrella?' 'How did he get in without me noticing?' And, most importantly, '_How the fuck does he know about the Tylenol?_'

Oliver turned, the capsule still in hand, to look at the intruder, his saviour, if you want to romanticise it.

The man walked into the room with a sense of importance. Abbie disliked him immediately, not only had he spoiled her plans, her birthday treat to herself, her first murder, but now he was looking at her like he _owned _her. Like she was a naughty child.

Oh, actually, she more than dislike him.

She hated him.

He smiled and pointed to the door with his umbrella, "Miss Smith," he said with a condescending smile, "There is a car waiting downstairs for you. We will take you home, and then you and I will have a little chat."

While he had been saying this two other men, also in suits, had entered Oliver Carter's dining room and taken the wine, both glasses, the bottle of Tylenol and plucked the killing-capsule right out of Oliver's hand. Oliver had sat there the entire time, dazed. With a confused look on his face, wondering who these people were, and why they were in his dining room, ruining his date.

He didn't say anything though, Oliver Carter wasn't so stupid that he couldn't see that the man in front of him clearly out ranked him, in every sense of the word.

At this point the man turned to Oliver and gave him a once over. "Mr Carter, Miss Smith did not arrive for your date tonight, she cancelled last minute, she has an emergency situation to attend to, and won't be back for some time. You will inform no one of what actually transpired here tonight. If you do, well," with his right arm he gestured around himself, "I know where you live." Oliver's eyes widened and he gulped. His mouth was very suddenly very dry, and he found himself unable to speak, so he just nodded. This seemed acceptable to the man, so he gave Oliver a condescending smile as well, "Good boy." And swept out of the room, beckoning Abbie to follow him.

Now, Abbie did not want to follow this man. She wanted to stay exactly where she was, and, given her new pissed-off mood, fuck subtly she wanted to stab Oliver several times in the throat.

But she didn't.

She knew that if she didn't do what this man told her, she would be going to prison for attempted murder, considering he knew what she'd done with the wine and the Tylenol. Speaking of,

_How did he know what she was up to?_

For self-preservation, and for curiosity's sake, Abbie followed this mysterious man out of Oliver Carter's house and into the black BMW waiting on the curb for her.

The car ride home was silent. Abbie spent it observing her new companion. He sat upright, his back poker-straight, and he looked out his window at the civilians on the street with a sense of ownership. Like he was king of all he surveyed.

Abbie really, really hated him.

Upon arriving at her house Abbie flung the door to the car open with such force it knocked over Mr Clancy, an elderly gentleman who lived a few doors down.

If Abbie cared about keeping up appearances she would've stopped, apologised profusely and helped Mr Clancy to his door.

But she didn't.

Who cares what some 70-somethig retired gardener thought of her?

Now she had bigger fish to fry.

The man also ignored Mr Clancy and left his chauffeur to help the assaulted OAP back to his feet

When she reached her sitting room she threw herself down on her sofa and glared at this man, this spoiler of plans, this pompous asshole, and demanded;

"Who the fuck are you, and how did you know?"

"My name, Miss Smith, is Mycroft Holmes. And if you are referring to the murder you were planning on committing tonight, I know because we've been watching you."

Abbie's eyes flared with anger, "How have you been watching me? I know when I'm being watched, no one's been tailing me for months!"

"No, you made it obvious that you could detect our agents, playing your little games with them. So, we decided on a, less direct means of tailing you."

He snapped his fingers and one of his, bodyguards, for lack of a better word, handed him a file. Mycroft Holmes threw the file to Abbie, and when she opened it, all the colour drained out of her face.

CCTV, they were tracing her using security cameras. They also had bank statements, credit card bills, phone bills, copies of her text messages, everything.

They noticed her stealing the cyanide out of the evidence room at the police station, they must have got copies of the tape before she erased it, they would have had no more than ten minutes to do so. They were good, clearly. And she had made a mistake.

She had made a mistake, she had miscalculated, she hadn't counted on this. Hadn't prepared for this, she was trapped.

In a matter of seconds, however, she was calm. 'Ok,' she thought, 'they're clearly not here to arrest me. They want something from me.'

So Abbie casually tossed the file on her coffee table and fixed Mycroft with a steady gaze, he winced, she was calm, collected, and ready to bargain.

Her stare was intense, for once in his life Mycroft Holmes felt like he was the one being examined, and he didn't like it.

"So, what _are _you going to do with me Mr Holmes?" Abbie grinned, crossing her legs and leaning back on the sofa.

"Well, there are two options Miss Smith. One, you can go to prison for attempted murder. But that's and something neither of us want to happen. Option two, which I would urge you towards, is to take a deal." Mycroft snapped his fingers again and was handed another file, which he threw on top of the first on the coffee table. Abbie picked up the file and scanned it. Inside were pictures of a number of crime scenes along with accompanying police notes, coroner's reports etc. And the first word that came into Abbie's head when examining the evidence was '_immaculate_.'

Everything was perfectly calculated, the correct drug dosage was found in each of the victims, measured out for their individual height and weight, to immobilize them, but keep the pain receptors working. They were then tortured methodically, dissected with surgical precision, having their heart removed. Likely they were still alive during the dissection, but would have passed out from the pain, and then died either from bleeding out, unless they'd had their heart removed before that could happen.

The perpetrator of these crimes left no trace of themselves, not a hair, not a fingerprint, nothing. _Genius._

This man, (and she was just judging it was a man due to the style, women tend not to be as, gory. They can be, but Abbie decided on the law of averages, it's a man.) Was a serial killer who knew what he was doing. No wonder Mr Holmes wanted help.

"So what do you what me to do?" Abbie asked, closing the file and tossing it casually on the desk, outwardly she appeared calm, nonchalant, disinterested even. On the inside however, she was desperate to get involved, go to the crime scenes, see for herself first-hand the murders, admire the handy work of this genius, and maybe even pick up a few tips…

Mycroft was feeling very disconcerted. He couldn't see all that was going on inside Abbie's mind, couldn't get a read on her at all. He wasn't used to this, this level of disassociation. Even from her clothes you couldn't tell that she had anything planned for this evening other than a pleasant dinner with Mr Carter. A master of disguise, that was what he was dealing with. A wolf in sheep's clothing, a psychopath, who to those who didn't have access to her medical or criminal records, would see nothing but a sweet and innocent girl.

The thought of this genuinely terrified Mycroft, that if he hadn't got the information that he had, he would walk past her in the street and suspect _nothing_. Then he smirked,

What fun Sherlock was going to have working with her.


	3. Chapter 3

**Chapter Three – Introductions**

Sherlock stood still for a moment, one hand pressed against his forehead, the other bawled in a fist around a sheet of paper, on which where several words, scrambled thoughts, none of which John had understood when he'd caught a glimpse of it. He'd never seen Sherlock struggle so badly with a case, not be able to get any readings at a murder scene, not able to analyse, not able to make assumptions about the killer. It was frustrating him. It was getting to a point where Sherlock no longer was enjoying this case, the killer was striking weekly, seemingly at random, and always with precision, no room for error.

Sherlock had worked out that whoever he was (Sherlock guessed it was a man due to the style, women tend not to be as, gory,) he was a psychopath. It was the only reasonable explanation as to why he couldn't work it out, why he couldn't crack this case.

It'd been two months, and Sherlock was making no head way with it. London was in panic. The seemingly random pattern that the killer was following meant anyone and everyone was a target, people were scared to leave them homes, the situation was dire.

Suddenly Sherlock roared and threw the crumbled piece of paper across the room, making John flinch. Mrs Hudson came scurrying up the stairs, but John waved her back down from his position on the sofa. No point in her coming up, Sherlock would just shout at her.

"Why! How! What is he! Aghhhh!"

Sherlock threw himself down in his chair, his head in his hands. He massaged his temples and sighed.

"Watson, I don't have the answers this time."

He leaned back in his chair and stared at the ceiling. John looked at the ground.

"I know, Sherlock, this is the toughest case you've ever had to tackle, we're not even at half time." He looked up at his friend, "But the game is on_, _Sherlock, and you're the only man in England who can solve this." _If anyone can, _John added in his thoughts, but dared not say that part out loud. Sherlock was already doubting himself, and needed no encouragement to sink into melancholy. "Isn't Mycroft doing… something?" Mycroft had come by a few weeks previous, and said he was working on something that may help them out. He was very vague, however, and whatever he was working on was yet to appear. Sherlock rolled his eyes and then closed them,

"Yes, 'something', god-only-knows-what, which will come god-only-knows-when, I wouldn't rely on Mycroft's 'something' Watson."

"Oh, little brother, what faith you have in me."

Sherlock's eyes shot open and he focused on the doorway, there stood Mycroft, behind him was a girl with long, brown, slightly curly hair and bright green eyes. She worked for Mycroft, his new secretary, he supposed.

Mycroft walked into the apartment and occupied Watson's usual chair opposite Sherlock. The girl perched on the sofa beside Watson. She gave him a small smile, which he returned, she seemed rather sweet to him, and he regretted that she had to work for Mycroft, he supposed the older Holmes wasn't exactly easy to work with, much like his brother.

"So, brother dear," said Sherlock, with an air of disdain, "What is this 'something' you've been working so tirelessly on?" Mycroft smiled, and gestured to the girl on the sofa, "Sherlock, meet Abigail Smith, she prefers to be called Abbie." Sherlock's eyebrows rose half-way up his forehead, he glanced at the girl, _nothing special,_ was how he summed her up.

"What? All this to get me a, what, a secretary?" he asked incredulously, Watson glanced once again at the girl beside him, what could she possibly have to do with this case?

Mycroft smirked, "why don't you analyse her?"

"Do we really have time for games?" Sherlock shot back,

"Indulge me, brother."

Sherlock sighed in defeat, and turned his attention to Abigail 'Abbie' Smith.

"You work in an office of sorts, as a secretary, you had coffee and muesli this morning for breakfast, I'm assuming from the way you're sitting you were brought up in a prim-and-proper home, in a fairly ordinary setting, you're well educated, intelligent, you like to take care of your appearance suggesting you care a great deal about what others think of you –" and then Sherlock was cut off, as Abbie leaned forward and smiled, this smile was seductive, suggestive… _predatory_, and not in line with what he'd read from her at all. He looked back at Mycroft, his eyebrows getting dangerously close to his hair line. Mycroft smiled at Sherlock in that condescending way he had always done, "Abigail Smith is a diagnosed psychopath, brother dear. A wolf in sheep's clothing, a master of disguise. And she can help you get inside the mind of your serial killer."

Mycroft reached inside his brief case and handed Sherlock a file, Abbie's file. This gesture didn't go unnoticed by Abbie either, _He's worried for his little brother, _she mused, Mycroft glanced over at her and made eye-contact, she smirked "What's wrong Mycroft? Scared of leaving Shirley with the big bad wolf?" she lounged back on the sofa, crossing her arms and legs, and smiled in a playful kind of way.

Watson mentally took back everything he'd thought about this girl, if one thing was certain, she was not sweet.

Sherlock flicked through her file, and was taken completely by surprise. He was completely and totally off with her history, her personality, everything. He'd read her so, so wrong. He looked up at Mycroft, "Are you sure this is a good idea? Letting her near this?" he inquired, the last thing he needed was her teaming up with the serial killer, two psychopath's running amok in London? Right now, that was his worst nightmare. Mycroft glanced down and sighed, "No, no I'm not sure," he looked over at Abbie, "but it's the only option we've got now Sherlock."

Sherlock stood up and placed Abbie's file on the desk, and met her gaze with an equally intense one, trying to analyse something, anything, about who she really was.

"One question, Miss Smith."

"Yes, Mr Holmes?"

"Was I right about the muesli?"

"Yes."

"Right, she's on the case." Sherlock clapped his hands and rubbed them together, "The game is on!"

Watson rolled his eyes, why did he hang out with these people?


	4. Chapter 4

**Authors note: **Hey! Terribly sorry it's taken me so long to update, I've been very busy the past couple of months!

But fear not! For those of you who are still interested in the story, chapters should be coming thick and fast from now on!

I really hope you enjoy!

**Chapter four – Having fun?**

Abbie woke up the next morning with a groan. She had slept in what she'd been informed was Watson's former room, and she just couldn't understand how he'd stayed in there, on that mattress! She stood up and opened the curtains, the sun was just peeking out over the tops of the building, she opened the window out and hung out the window for a moment, letting the early morning breeze hit her face. She moved back into the room and retrieved her cigarettes from her bag. Resting on the windowsill she lit up and reflected on the events of the night before.

After Mycroft had left her with his brother, and his side-kick, she had decided to keep her mouth shut, and let them do the talking, easier to observe when you're not required to join in the conversation.

From what she had gathered, this Sherlock was a pompous asshole who needed taking down a few pegs. He believed himself to better than everyone else in the room, much like his brother.

Yeah, she disliked this Holmes too.

And Watson, he was just like a little fan-boy. It was hard for her not to laugh at him, the way he idolised his friend.

But then again, Sherlock seemed to really, _care _about what Watson would say to him, yes, even if Sherlock would be abrupt with him, cut him off and put him down, he still seemed to care.

Oh, how she was going to have fun with that.

After finishing her cigarette she meandered into the kitchen to find Sherlock already sat at the table, he looked like he was, dissecting an eyeball? Okay, childish stuff, Abbie shrugged. She leaned over the edge of the table, making sure to invade the man's personal space, he winced, and she knew she had achieved the desired effect.

'Where'd you keep your coffee Shirley?' She grinned.

'Um, top shelf, above the kettle.' He said, turning away from her and retrieving a mug from the draining board, handing it to her without making eye contact.

He was uncomfortable, good.

Abbie didn't say anything more to him as she made her coffee, nor did she speak as she leant against the counter drinking it, observing him dissecting the eyeball.

Sherlock shivered, he could feel her eyes on him. It was a little ironic that it was those eyes that bothered him, meanwhile the average person would be more perplexed with the one he was cutting up.

But then again, neither of them where average, were they?

He finished playing with the eye, putting it in a tuber ware container and placing it in the fridge. He then took a deep breath and turned to face Abbie, expecting her to still be by the counter, but 'lo and behold, while he'd been putting the eyeball in the fridge, she'd moved to sit on the table. Right behind him. He exhaled in surprise, and she giggled. _She giggled. _'She's playing games with me,' Sherlock thought to himself, and it bothered him greatly. He was the game player, he observed people, he analysed them, _he_ played _them. _Not the other way round. But if she wanted to play, he was going to make it a good game. He smiled widely, 'So, Miss Smith,' he said, moving around her, as he passed he got a whiff of nicotine, great, she was a smoker, as if he needed any more temptation to whip out his emergency pack. 'Um, Miss Smith,' he turned around to face her general direction as he reached the archway between the kitchen and the living room, not meeting her eyes, looking anywhere but her. 'Watson will be arriving soon, then I have to nip out for a few things, he will keep you, company, while I'm gone, then when I get back we're heading to the latest crime scene, as you know the serial killer struck again yesterday morning, so you're going to, uh, go over the scene, see what you can pick up.' He smiled again, looking up she held his gaze, a smirk on her face, ah, yes, he hadn't exactly covered up how uneasy she made him feel very well. In fact, he hadn't kept it hidden at all. Damn, he was losing this game, badly.

Abbie was greatly amused, so, Shirley was going to leave her alone with Watson? He was clearly uncomfortable with the idea, (well, he was uncomfortable with her very presence.)

Maybe she should confirm his fears, give him a reason not leave her alone with his little friend….

Ah, she was going to have fun.

It wasn't long until John arrived, Abbie whiled away the time by playing with Sherlock. He would attempt to make conversation with her, trying to avoid the uncomfortable moments where she would just stare at him, like a cat staring at its food. As a matter of fact, Sherlock very much felt like Abbie was playing with her food, and he was on the menu.

Abbie found it hilarious that he was trying so very hard to not let her get to him, but it was too late, she'd already got under his skin. She had established that last night, when he would fidget profusely while talking to Watson, his eyes fixed on him, determined _not_ to look at her.

As if there was any more of a give away.

When Watson arrived Sherlock dashed down the stairs, muttering something about greeting him,

Hah, bullshit.

He was warning Watson. He was definitely regretting the decision to have him babysit her, but it was too late to go back on that, then Abbie would have won.

She couldn't hear what he was saying to dear John, but she could guess. It would be along the lines of 'don't trust her, your life depends on it, don't believe anything she says, don't accept anything she gives you, not so much as a cup of tea,' etc. etc.

But she would get to Watson, she wouldn't kill him, no that would be stupid, then the deal would be off. She would go to prison, and she wouldn't get to explore the crime scene. And she was so very eager to go see that genius's work, to look upon his latest masterpiece.

So no, she wouldn't kill Watson, she was just going to have some fun…


End file.
